The present invention relates to a control apparatus of an optical disc player for optically recording video information or audio information on an information track formed on the record medium and for reproducing the signal recorded on the information track. The present invention relates, in particular, to a player which has a device for discriminating a track having no signals recorded thereon and which has a function of correctly searching a track having no signals recorded thereon by rapidly moving a signal recording/reproducing means on the recording medium prior to additionally recording an information signal on the track having no signals recorded thereon.
An example of a conventional apparatus for recording/reproducing the video information or the audio information is an optical recording/reproducing apparatus such as an optical video disc player or an optical audio player which records/reproduces the information using an optical approach. That apparatus has a function of focusing a light beam generated from a light source onto a disc-shaped record medium (hereinafter referred to as a disc) to record signals in a concentrical or helical form on the disc and has a function of detecting the reflected light fed from the disc to read this signal recorded on the record medium. FIG. 1 shows a block diagram of that optical recording/reproducing apparatus.
A disc 1 is a medium for recording the information and is rotated at the rate of 1,800 rpm, for example, by a disc rotating motor 2. In an information recording operation, the video signal fed from a TV camera or the like is subjected to frequency modulation in a record modulation circuit 3 to be carried over a carrier frequency belonging to a desired frequency band. In accordance with the signal thus modulated, a laser drive circuit 4 varies the current flowing into a laser diode 5. The intensity of the light beam emitted by the laser diode 5 is thus varied. The light beam is used to record the signal on the disc 1. Owing to the use of a laser diode as a light source, a single light source suffices to record and reproduce the information. As a result, it is possible to reduce the overall size and dissipated power of the apparatus. In addition, direct modulation and control of the recording light beam may be easily carried out. The light beam generated by the laser diode 5 is passed through a lens 6 and a semitransparent mirror (half mirror) 7. The direction of the light beam is altered by a mirror 8. The resultant light beam is focused onto the disc 1 placed over the disc rotating motor 2 by a condenser lens 9. The light beam reflected by the disc 1 is passed through the condenser lens 9. The direction of the light beam is then altered by the mirror 8 and the semitransparent mirror 7. After passing through a lens 10, the light beam is divided into two parts by a mirror 11. One part is fed to a pair of photosensitive diodes 13a and 13b and the other part is fed to another pair of photoresistive diodes 12a and 12b. Signals fed from photosensitive diodes 13a and 13b are respectively fed to amplifiers 17c and 17d to be amplified. The signals thus amplified are fed to a differential amplifier circuit 18 to yield the difference between them. According to the difference signal, a well known focus control unit controls the position of the condenser lens 9 so that the diameter of the focused light beam will be approximately 1 .mu.m. On the other hand, signals fed from the photosensitive diodes 12a and 12b are amplified by amplifiers 17a and 17b and then fed to a differential amplifier or subtracter 24 to yield the difference signal between those signals. The difference signal or tracking control signal drives a tracking control signal generating circuit 25 and a drive circuit 26. The angle of the mirror 8 attached, to the tracking control element 14 is varied so that the light beam focused onto the disc 1 may correctly scan signals on the track, resulting in tracking control.
When the information recorded on the disc 1 is to be reproduced, the optical output of the laser diode 5 is set to a value is lower than its optical output value in the recording operation. The light beam generated by the laser diode 5 is passed through the intermediate lens 6 and the semitransparent mirror 7 in the same way as in the recording operation. The direction of the lgiht beam is then altered by the mirror 8. The condenser lens 9 focuses the light beam onto the disc 1. The light beam reflected by the disc 1 is passed through the condenser lens 9 again. The direction of the light beam is then altered by the mirror 8 and the semitransparent mirror 7. After passing through the lens 10, the light beam is split into two parts by the mirror 11. One part is fed to photosensitive diodes 13a and 13b to be used as the reproduced video signal and the focus control signal. The other part is fed to photosensitive diodes 12a and 12b to be used as the tracking control signal in the reproducing operation. The signals sent out from the photosensitive diodes 13a and 13b are added in a summing circuit 19. The resultant sum signal or modulated video signal is fed to a video signal reproducing circuit 20 to demodulate the original video signal. The video signal thus reproduced includes an address signal corresponding to a track which is recorded in the vertical blanking line period, for example. An address discrimination circuit 21 reads out the address signal of the record track and feeds it to a microcomputer 22.
Referring to the conventional circuit illustrated in FIG. 1, the operation for searching a desired track on the disc 1 will now be described. An address corresponding to a desired track is specified through a keyboard 23. Thereafter, a start instruction is inputted using keys arranged on the keyboard 23. The microcomputer 22 calculates the difference between the specified address and the current track address fed from the address discrimination circuit 21. The resultant difference is preset into a coincidence detection circuit 28. The coincidence detection circuit 28 is usually composed of an up/down counter and a digital-analog converter. The output signal of the counter is converted into an analog voltage by a digital-analog converter (hereafter abbreviated as DAC). The resultant analog voltage is fed to a motor drive circuit 29 to drive a motor 30. The motor 30 in turn moves a movable table 16 in the radial direction of the disc 1. Each time the light beam focused by the condenser lens 9 crosses a track during the movement of an optical system 15 placed on the movable table 16, a waveform shaping circuit 27 provided for shaping the waveform of the output signal from the differential amplifier 24 produces a pulse signal. This pulse signal is fed to the counter included in the coincidence detection circuit 28 in the down mode. The speed of the motor 30 is controlled by the output voltage of the coincidence detection circuit 28.
In summary, when an additional signal is to be recorded on a track of the disc 1 having no signals recorded thereon, address signals recorded beforehand on portions corresponding to vertical blanking line periods are detected to search for a desired record track. The prior art has the following problems.
(1) Since the optical system 15 must be moved while detecting address signals, high speed transfer of the optical system 15 is difficult, resulting in a long search time.
(2) If the current address is not detected as a correct value, the optical system 15 passes a desired track, necessarily bringing about a long search time.
(3) The prior art is not applicable to a disc having no addresses recorded beforehand thereon.